Question 50·Medium·Command of Evidence
The following bar graph shows the percent yield of isoamyl acetate produced in an esterification reaction under two mixing conditions. For each mixing condition, one trial used a small amount of sulfuric acid as a catalyst (dark bars) and one did not (light bars).
To test whether the catalyst increases product yield, a student compared the percent yields across the four trials. The student concluded that the higher percent yields in the trials with the catalyst were entirely attributable to the presence of the catalyst.
Which choice best describes data from the graph that weaken the student’s conclusion?
For command-of-evidence questions about conclusions, zero in on extreme language like entirely or only. Then scan the graph for a pattern that introduces an alternative explanation (here, a change in yield when the catalyst stays the same). Finally, select the choice that describes that specific data pattern accurately, not just a true statement about the graph.
Hints
Focus on the strong wording
The conclusion says the difference is entirely due to one cause. Look for any evidence that something else matters.
Compare the same color bars
To isolate the effect of mixing, compare the two light bars (no catalyst) across the two mixing conditions.
Pick the option tied to that comparison
Choose the option that points to a clear yield change that happens even when the catalyst is not present.
Step-by-step Explanation
Identify what would weaken the claim
The conclusion uses the strong phrase entirely attributable, so evidence that another factor affects yield would weaken it.
Check whether mixing affects yield without the catalyst
Look at the light bars (no catalyst) for both mixing conditions: the percent yield is much higher when the mixture is stirred than when it is unstirred.
Match that evidence to the best choice
The option that states stirring raises yield even without the catalyst best challenges the idea that the catalyst alone explains higher yields.
Therefore, the correct answer is: Without the catalyst, stirring still raised the percent yield by more than 20 points compared with leaving the mixture unstirred.